Ultraviolet light has been found useful for irradiating living tissue such as human skin for purposes such as tanning and for destroying microorganisms for sterilization purposes. Ultraviolet (UV) irradiation, which is outside the visible spectrum and which has a wavelength in the range of 100-400 nanometers (nm) has been informally classified as UV-A, having a wavelength in the range of 315-400 nm, UV-B, having a wavelength in the range of 280-315 nm and UV-C, having a wavelength in the range of 100-280 nm. Heretofore, UV-B has been that which is employed widely for irradiating human skin for tanning or cosmetic purposes and for use as a germicidal.
The more common sources of UV-B radiation have heretofore been lamps having a tubular configuration using an enclosed low pressure mercury arc source enclosed within a quartz or fused silica glass tube with the interior surface of the tube coated with a phosphor material for fluorescent conversion of emitted radiation.
In using UV radiation for tanning purposes UV-B and UV-C below 300 nm have been found to present a danger of over irradiation producing burning of the living tissue; therefore, lamps intended for such purposes are generally restricted below 10% UV-B to UVA irradiation. UV-A emanating from solar radiation is known to have deeper dermal penetration that destroys DNA and vitamin D3 in cellular tissue, and is thus to be avoided for such usage.
FIGS. 1 and 2 show typical examples of the spectral power distribution of presently commercially available UV-B lamps for which it is noted that a large majority of the power is less than 40% in any narrow frequency range which results in limited effectiveness of the lamps for the aforesaid purposes.
Therefore, it has been desired to provide equipment for generating UV-B irradiation that has the optimal benefit for use with living cellular tissue and as a germicidal without increasing the risks of damage to the living tissue.